Hello, I am a solicitor with over 15 years experience. I will try to answer your question.
This is not necessarily the case. If the reason fro the run off is the fault off the developer/occupier then you may well be able to claim compensation or get alterations carried out to the neighbouring land to end the problem. Raising land will obviously lead to alterations in where and how water runs off. It may be that insufficient account was taken of his risk when the work was carried out.
When was the work carried out and have the new properties been sold? Do you know how to contact the developers? Your first step will be to contact the developer and/or occupiers to let them know about the problem and inviting them to investigate.